1. Field of the Invention
The present invention relates to a camera module, and more particularly to a relatively small camera module to be mounted on an electronic apparatus, such as, for example, a cellular phone.
2. Description of the Prior Art
A relatively small camera module is mounted on an electronic apparatus, such as, for example, a cellular telephone. Such a camera module includes an image pickup device, such as, for example, a CMOS sensor or a CCD sensor. FIG. 1 illustrates a cross-sectional view of a conventional camera module 11, and FIG. 2 is a plan view illustrating a base 131 and an IR cut filter 14 in the conventional camera module 11. FIG. 1 is a cross-sectional view taken generally along a line I-I of FIG. 2. As shown in FIG. 1, the camera module 11 has a lens unit 12 and an image pickup portion 13 provided under the lens unit 12.
The lens unit 12 includes a first lens 123, a second lens 124, a barrel 121 provided with the first lens 123 and the second lens 124 therein, and a lens holder 122 for rotatably holding the barrel 121. When the barrel 121 is rotated with respect to the lens holder 122, the barrel 121 is moved in a direction of an optical axis so that a focus adjustment is carried out.
The image pickup portion 13 includes a base 131 having a substantially rectangular opening 134 formed in an upper surface of the base 131, an IR cut filter 14 disposed so as to cover the opening 134 in the base 131, a substrate 16 provided below the base 131, and an image pickup device 15 of a CMOS sensor mounted on an upper surface of the substrate 16. As shown in FIG. 1, a housing space 133 for housing the CMOS sensor 15 in a hermetically sealed state is formed within the base 131. The housing space 133 is defined by the base 131, the IR cut filter 14, and the substrate 16.
The base 131 has an overhanging portion 135 for supporting the IR cut filter 14 around the opening 134. The overhanging portion 135 is illustrated as extending inwardly toward the housing space 133 in a horizontal direction with respect to FIG. 1. As shown in FIG. 2, peripheral edges of a rear face of the IR cut filter 14 are bonded to a support portion 132a which is located around the opening 134 in the base 131. The support portion 132a is provided at a position lower than the height of an upper surface 132b of the overhanging portion 132. A plurality of recesses 132c, 132d are formed outside of the support portion 132a. A resin adhesive is dropped into the recesses 132c, 132d. As shown in FIG. 1, each of the recesses 132c, 132d has a bottom surface 132g inclined from the upper surface 132b of the overhanging portion 135 toward the support portion 132a. 
The peripheral edges of the IR cut filter 14 are bonded to the support portion 132a of the overhanging portion 135 with an adhesive. The bonding operation is conducted by dropping a proper amount of resin adhesive into the recesses 132c, 132d with use of a syringe. The resin adhesive dropped in the recesses 132c, 132d is guided by the inclined surfaces 132g of the recesses 132c, 132d and impregnated into gaps between the peripheral edges of the IR cut filter 14 and the support portion 132a. As a result, the IR cut filter 14 is bonded to the overhanging portion 132.
In the conventional camera module 11, when the peripheral edges of the IR cut filter 14 are to be bonded to the support portion 132a of the overhanging portion 132, it is necessary to strictly adjust the amount of resin adhesive to be dropped into the recesses 132c, 132d. Specifically, if the amount of resin adhesive dropped into the recesses 132c, 132d is larger than a proper value, the resin adhesive cannot remain in the gaps between the peripheral edges of the IR cut filter 14 and the support portion 132a and leaks into the opening 134 of the base 131. Alternatively, if the amount of resin adhesive dropped into the recesses 132c, 132d is smaller than the proper value, the resin adhesive cannot be impregnated into all the gaps between the peripheral edges of the IR cut filter 14 and the support portion 132a. As a result, the housing space 133 cannot maintain a hermetically sealed state to prevent dust from being attached to surfaces of the image pickup device 15.
Further, when the resin adhesive is adjusted so as to have a high viscosity in order to control the impregnation of the resin adhesive, the resin adhesive becomes unlikely to be impregnated into the gaps between the peripheral edges of the IR cut filter 14 and the support portion 132a. Alternatively, if the resin adhesive is adjusted so as to have a low viscosity, the resin adhesive leaks into the opening 134 of the base 131.
In order to resolve the above-mentioned problems, a skilled operator has to adjust a syringe manually during the bonding operation. However, the skilled operator has to await completion of the impregnation of the resin adhesive in order to confirm that the resin adhesive has been impregnated into the gaps between the peripheral edges of the IR cut filter 14 and the support portion 132a and has not leaked into the opening 134 of the base 131. Accordingly, it takes several minutes after completion of dropping a resin adhesive with use of a syringe to know whether a proper amount of resin adhesive has been dropped into the recesses 132c, 132d. This period of time required for confirmation lowers a working efficiency of the operator.
Further, the impregnation of the resin adhesive is also affected by other factors such as a temperature of a room in which the bonding operation is conducted. Accordingly, the amount of resin adhesive to be dropped into the recesses 132c, 132d should be adjusted according to factors, such as, for example, a temperature of a room in which the bonding operation is conducted. Thus, the adjustment of the amount of resin adhesive has to depend on experience of the skilled operator.
As described above, it is very difficult to adjust the amount of resin adhesive to be dropped into the recesses 132c, 132d. Further, such adjustment requires a skilled operator. Thus, efficiency of the bonding operation is lowered, and a manufacturing cost of the camera module is increased.